A woman has milk poured in her eyes after being sprayed with a chemical irritant. (Getty Images)

Dueling pro- and anti-Trump rallies in Berkeley, Calif., turned violent Saturday as numerous fistfights broke out and protesters fired pepper spray into a crowd. Police arrested more than a dozen people and requested aid from other law enforcement agencies.

It was not immediately clear what protesters were charged with, or whether there would be more arrests. The Berkeley Police Department seized numerous prohibited items, including sticks and knives, according to the agency.

In anticipation of the protests at Civic Center Park in downtown Berkeley, the agency had banned items that could be used as weapons, such as pepper spray, mace, baseball bats and glass bottles.

Hundreds of people gathered at the park for a pro-Trump rally and a counterprotest, some dressed in black and wearing masks, the Los Angeles Times reported. There were loud explosions and fistfights among members of both groups, and a citizen militia group wearing security gear showed up to protect the pro-Trump demonstrators. Berkeley police officers, wearing riot helmets, separated pro- and anti-Trump attendees, the Times reported.

Photos and video of the protests showed some protesters were bloodied and injured. But other protesters walked along with the crowd quietly holding signs, or chanting about free speech.

The rallies appeared to be separate from the dozens of protests in cities throughout the country calling on Trump to release his personal tax returns as part of a nationwide Tax March.

Groups of demonstrators have had similar clashes before. On March 4, a mixed crowd of about 500 pro- and anti-Trump demonstrators similarly became violent. Fistfights broke out, and protesters used pepper spray, metal pipes, lumber, bricks and other items that were prohibited for Saturday’s protests. Ten people were arrested during the March 4 protests on charges of battery, assault and resisting arrest, according to local news reports.

In February, the University of California at Berkeley canceled a scheduled talk by former Breitbart News editor Milo Yiannopoulos after intense violence and vandalism broke out on campus.

On Twitter, Berkeley police warned the public to stay clear of the protest area. City officials had shut down a farmers market in the park in anticipation of Saturday’s rally, and warned against vandalism and violence.

A man is sprayed with a chemical irritant as multiple fights break out between Trump supporters and anti-Trump protesters in Berkeley, Calif., on Saturday. (Getty Images)